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Safety and Epilepsy: Photosensitive epilepsy and the flashing lights during the holidays

Most of us have heard that flashing lights can be a trigger to epileptic seizures. Probably the most famous case of seizures triggered by flashing lights happened in 1997 when nearly 700 children ended up in the ER in Japan after watching a Pokémon cartoon. 

What do we need know about flashing lights as potential triggers of seizures during the holiday season?  Dr. Olgica Laban-Grant helps us understand all about the risks of flashing lights.

What is photosensitive epilepsy and how many people are estimated to have this form of epilepsy?

Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual patterns such as flashing lights, and bold, contrasting visual patterns. About 3% to 5% people with epilepsy will have photosensitive epilepsy. This type of epilepsy is more common in children and adolescents (10% of patients with epilepsy ages 7-19), in girls (60%) and in certain epilepsy syndromes. There is also a genetic predisposition to this type of epilepsy and therefore several family members may be affected. Although many people may feel disoriented or uncomfortable when seeing flashing lights this does not mean that they have photosensitive epilepsy. Photosensitive epilepsy can be diagnosed by abnormal EEG (electroencephalogram) while preforming photic stimulation (exposure to strobe lights at different frequencies).

Is there a particular speed of flashing that represents a danger and are most holiday lights safe?

Flashing lights at frequency between 16-25 hertz (flashes per second) are the common rates that trigger seizures but this varies from person to person. There are people who can be sensitive to frequencies from 3Hz up to 60Hz. There are certain characteristics of patterns that are more likely to trigger seizures such as patterns that are high in luminance contrast (for example black and white stripes, and checkerboard patterns), stimuli that fill the larger portion of visual field and that are seen by both eyes. Certain people may be more sensitive to some colors (especially saturated red) or color combinations (particularly red-blue). Therefore closing both eyes does not prevent photosensitive reaction but on contrary may increase risk because of red-tinted light filtering through the eyelids. The Pokémon sequence mentioned above was 4 seconds long, with flashing red and blue fields, at a frequency of 12.5 Hz occupying the entire screen.

There are also a lot of flashing lights everywhere in November and December on Christmas trees, houses, streets, awnings, etc.  Some New Year's parties might also include strobe lighting.  Should people living with epilepsy be concerned and do they need to take special precautions at this time of year?

Unfortunately strobe lights at performances or in nightclubs, even fireworks if it is flashing at high enough rate, and many cameras flashing at once may produce rate of contrast/flashing light that may trigger seizures. Holiday lights usually flash at low frequency (under 2Hz), and are therefore too slow to cause a seizure. However, if several circuits are flashing together or there is malfunction of the lights this can accidentally increase the flash rate. 

Is there anything that someone with photosensitive epilepsy can do to stay safe avoiding triggering a seizure through lighting?

There are certain precautions that may be taken in addition to common precautions:

When outside, wear polarized sunglasses to protect your eyes from bright light (this will reduce but not eliminate photosensitivity). Watch TV and play video games in a well-lit room and at a safe distance from the screen (at least 8 feet from the TV and 2 feet from a computer monitor). Use flicker-free monitors and reduce the brightness on monitors. Take regular breaks from the screen exposure. If you are accidentally exposed to flashing lights/contrast images close/cover one eye (do not close both eyes or open and close eyes as that can increase your risk), turn your head away and remove yourself from that environment.

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